1. Technical Field
This invention relates to heating, ventilating, air conditioning, and refrigeration (HVAC/R) systems. More specifically, the invention relates to a demand ventilation module for HVAC/R systems and units to control indoor air condition levels, such as carbon dioxide (CO2) levels for example.
2. Background Art
In an effort to provide maximum energy savings, many buildings are designed to be as airtight as possible. This is generally accomplished by limiting the amount of outside air infiltration. However, it has since been discovered that this tight building construction contributes significantly to the excessive build up of indoor air contaminants from various sources. These contaminants affect the health of building occupants resulting in what has become known as Sick Building Syndrome (SBS).
Various scientific studies concluded that buildings should be ventilated with a specific amount of outside air, based on occupancy and potential pollutant levels in the space, in order to allow the concentrations of indoor air pollutants to be reduced to acceptable levels. To this end, the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) has established outdoor air standards that are usually adopted by most building codes and design engineers. Specifically, ASHRAE recommends ventilating buildings with different volumes of outside air based on a number of factors including potential pollutant levels and duration of occupant exposure encountered in specific applications.
To facilitate proper ventilation, previous strategies and products have been provided. A fixed air strategy has been provided to allow a fixed amount of outside air to infiltrate the building at all times through the HVAC/R system. This solution, however, results in excessive waste of energy when the room is not occupied and often overloads the HVAC/R system""s capacity to regulate thermal comfort. In addition, the HVAC/R fan must run continuously to provide continuous ventilation. Furthermore, conventional room thermostats have only two fan options: xe2x80x9cautoxe2x80x9d and xe2x80x9conxe2x80x9d. Both options are selected manually via a switch on the thermostat. When in the xe2x80x9cautoxe2x80x9d position, the fan cycles on and off with the heating or cooling demand. This means the HVAC/R fan and associated ventilation stop when the heating or cooling demand is satisfied. But when the fan selector may be xe2x80x9conxe2x80x9d, then the room may be constantly ventilated, even when unoccupied. Thus, the fixed air strategy wastes energy and adds more heating or cooling load to the HVAC/R system.
One present control strategy regulates the amount of outside air infiltration based on xe2x80x9cprojectedxe2x80x9d occupancy. The concept of this strategy is to reduce unnecessary ventilation by estimating when the room may be either not full or unoccupied. This control strategy requires someone to xe2x80x9cprojectxe2x80x9d or estimate expected occupancy levels and physically manipulate the control set point. This strategy often results in over-ventilating or under-ventilating the space when estimates are inaccurate.
Energy Recovery Ventilators have also been designed to force outgoing room air and incoming outside air to pass through an air-to-air heat exchanger before entering the air conditioning system. The strategy of these products is to transfer heat from one air source (the room) to another (outside air) in order to reduce load on the HVAC/R system. However, these products operate constantly, whether the room may be occupied or not, adding load to the system (over-ventilating) at times when the space may be not fully occupied or unoccupied altogether. Additionally, there is no provision to control the HVAC/R fan operation.
Accordingly, what is needed is a ventilation apparatus that overcomes the drawbacks of previous ventilation strategies and products, such as energy waste, increased heating or cooling load, increased maintenance and electrical consumption, noise, and the lack of HVAC/R operation control, through a demand ventilation module that regulates ventilation in direct proportion to actual occupancy of an inside space automatically.
The invention solves the foregoing and other conventional ventilation problems through a retrofit demand ventilation module for use with HVAC/R systems to facilitate compliance with ventilation requirements for acceptable indoor air quality. The demand ventilation module may utilize a control strategy known as xe2x80x9cdemand ventilationxe2x80x9d. This concept involves regulating ventilation dampers to provide the minimum required amount of outside air based on actual demand. For example, as inside space occupancy increases, the CO2 levels in the inside space increase in direct proportion to actual real time human occupancy due to the natural human respiration process. Conversely, when space occupancy decreases, the CO2 levels decrease. Accordingly, measuring the CO2 levels in the inside space and regulating an outside air intake damper may achieve significant energy reduction while still providing adequate ventilation for the occupants.
The demand ventilation module may be an apparatus configured to be coupled to any location on a return portion of a new or existing HVAC/R system (external to the HVAC/R equipment) and capable of drawing and regulating outside air into the HVAC/R system and into the inside space of a structure by way of an air pressure differential between return air and the outside air. The demand ventilation module may include a damper to regulate outside air infiltration into the HVAC/R system and into the inside space by way of the air pressure differential between the return air and the outside air. In some embodiments of the invention, the demand ventilation module may further integrate an optional air restrictor plate in conjunction with the damper that defines an air-restricting opening for more accurate control of the damper under low air velocity conditions. The damper and the air restrictor plate (if included) may be integrated into an inner chamber of a self-contained housing. The housing may include an air outlet and outside air inlet. The housing is configured to easily be coupled externally to any location on the return portion of the HVAC/R system and external to the HVAC/R unit itself.
The demand ventilation module may also integrate or associate remotely with an electronic control device configured to facilitate ventilation control and HVAC/R unit fan operation. The electronic control device may be capable of setting and storing pre-set minimum absolute air condition differential parameters (e.g., CO2 condition setpoints) for ventilation activation. The electronic control device may be communicationally connected to and able to coordinate and control the activation of an actuator in conjunction with inside sensors that measure air conditions (e.g., CO2 conditions). Upon receiving and comparing signals from the sensors to an air condition set-point, the electronic control device may cause the actuator to automatically shift the damper to any position in the damper stroke range in direct proportion to actual real-time air condition demands (i.e. occupancy levels of the inside space as evidenced by CO2 levels).
Once installed, demand ventilation modules may also be networked together with network communication connections into a system. This gives an operator the ability to fully coordinate and control and monitor multiple HVAC/R units on multiple buildings at multiple sites for example via interfacing through any form of communications connections with the demand ventilation modules.
Thus, an advantage of this invention is that it may provide a universal retrofit module with adjustable damper positioning in order to accommodate various ventilation requirements subject to specific applications. Therefore, the invention may be capable of retrofitting virtually any and all new or existing HVAC/R units and a wide variety of HVAC/R applications that have no or inadequate factory integrated provisions for automated fresh air intake. Another advantage of this invention is that it may provide HVAC/R equipment with a state-of-the-art computerized controls package capable of controlling, monitoring and trend logging virtually all aspects of HVAC/R ventilation operation, thereby providing maximum energy savings. Accordingly, the invention may provide continuous HVAC/R fan operation during occupied hours for continuous ventilation, while cycling the HVAC/R fan during unoccupied hours to save energy. Additionally, because in some embodiments the invention may be completely self-contained with integral control components, it may provide a simple and low cost installation, and simple and reliable quiet operation with a minimum of moving parts, thereby virtually eliminating mechanical maintenance and resulting in drastically reducing first cost and energy consumption.